Plugs made of rubber, elastomer or the like are conventionally used in order to seal bodily fluid collection tubes, such as a vacuum blood collection tube.
Patent Literature 1 below discloses an example of a plug of this kind. FIG. 9(a) is a partly cutaway front cross-sectional view for illustrating a plug described in Patent Literature 1. The plug 102 is attached to an upper end opening of a closed-bottomed, cylindrical, bodily fluid collection tube 101 to seal it. The plug 102 includes a plug body 103 made of rubber, elastomer or the like and a cover member 104. The plug body 103 includes a press-fit part 103a press-fitted into the bodily fluid collection tube 101; and a grip part 103b continued upward from the press-fit part 103a. The cover member 104 is fitted to the grip part 103b to cover the grip part 103b. 
The cover member 104 includes a head plate 104a engaging against the upper surface of the grip part 103b of the plug body 103. A skirt 104b is provided to extend downward from the outer peripheral edge of the head plate 104a. 
Alternatively, Patent Literature 2 below discloses a plug 111 shown in front cross-section in FIG. 10. The plug 111 includes a plug body 112 made of rubber, elastomer or the like and a cover member 113 fitted on the plug body 112. A press-fit part 112a of the plug body 112 is press-fitted into a bodily fluid collection tube 101. A grip part 112b continued upward from the press-fit part 112a is covered by the cover member 113.
An annular retaining ring 114 is placed on the upper surface of the grip part 112b. The cover member 113 has a tubular shape. An annular extension 113a is provided to extend inward from the upper open edge of the cover member 113. The retaining ring 114 is engaged to the annular extension 113a against slipping out upward.
The cover member 113 is provided at the middle of the height with an annular engagement ledge 113b extending inward from the inside wall of the cover member 113. The annular engagement ledge 113b is clamped between the lower surface of the grip part 112b of the plug body 112 and the upper end of the bodily fluid collection tube 101. Specifically, the grip part 112b is formed to have a larger diameter than the press-fit part 112a of the plug body 112, so that a shoulder 112c is formed on the lower surface of the grip part 112b. The annular engagement ledge 113b is engaged against this shoulder 112c. 
The cover members 104, 113 described in Patent Literatures 1 and 2 are provided to allow examining staffs to easily remove the plug bodies 103, 112 from the bodily fluid collection tubes 101 without touching the plug bodies 103, 112 with their hands. Specifically, by applying a force to the cover members 104, 113 with fingers to move it away upward from the bodily fluid collection tubes 101, the plug bodies 103, 112 can be removed together with the cover members 104, 113 from the bodily fluid collection tubes 101.